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Status Report, Vol. 38, No. 8 | August 26, 2003 Subscribe

Head-protecting side airbags reduce driver fatality risk by 45 percent

Side airbags with head protection have looked promising in crash tests like the one pictured above. Are they also saving lives in real-world crashes? Yes.

Now that tens of thousands of drivers have been involved in crashes of side airbag-equipped cars, the Institute has conducted the first study of the real-world effectiveness of this type of protection. The major finding is that side airbags with head protection are highly effective. They're reducing deaths among drivers of passenger cars struck on the near (driver) side by about 45 percent. Side airbags that protect the chest and abdomen, but not the head, also are reducing deaths. But these side airbags are less effective. They reduce deaths by about 10 percent.

Each year more than 9,000 passenger vehicle occupants die in side impacts. Head injuries are a leading cause. The new research findings mean the toll should be reduced in the future.

"The need to protect occupants' heads in side impacts has been obvious for some time, Institute president Brian O'Neill points out. "Before head-protecting airbags were available, there was virtually nothing to prevent people's heads from being struck by intruding vehicles or rigid objects like trees or poles in serious side impact crashes. Now we know side airbags can change this and do a good job of protecting people's heads.

Both the U.S. standard on side impacts (Federal Motor Vehicle Safety Standard 214) and the European standard specify test impacts in which dummies' heads aren't hit by the striking barriers. Another U.S. standard (Federal Motor Vehicle Safety Standard 201) requires padding in the interiors of vehicles where some people's heads hit in crashes. There are no protective requirements for heads in window areas.

"When people's heads are in the window they're vulnerable to being struck by intruding vehicles or objects in side impacts, O'Neill says. "The increasing number of high-riding vehicles on the road these days increases this risk, making it more likely that the front end of a striking vehicle in a side impact will hit the heads of occupants in the struck vehicle. This is why side airbags with head protection are so important.

Side airbags that protect the torso only don't represent as fundamental a safety improvement. They're one way to protect the chest and abdomen in a side impact, but not the only way. Padding also can be used to protect occupants' torsos.

Range of side airbag designs

Since the mid-1990s when Volvo introduced side airbags and BMW and others added head protection, more automakers have followed suit. By the 2003 model year, 40 percent of all passenger vehicle models offered head-protecting side airbags (standard equipment in 24 percent of models, optional in 16 percent).

Some passenger vehicles have combination head/torso side airbags. Other vehicles have two separate side airbags, one for the torso and another for the head.

Most of the torso-only and combination head/torso designs inflate from vehicle seats, although some inflate from the door. Side airbags designed exclusively to protect people's heads — so-called curtains or tubular structures — inflate down from a vehicle's roof area.

Types of side airbags

There are essentially three types of airbags designed to protect people's heads in side impacts.

Curtains descend from the roof of a passenger vehicle to protect the heads of occupants in both front and rear seats.

Inflatable tubular structures attached to the roof deploy along with separate side airbags designed for the torso.

Torso/head combination airbags deploy from vehicle seats, or sometimes from the doors, to protect both the torso and the head.

Crash test results

Since 1997 the Institute has been testing vehicles with various side airbag designs (see "Airbags for heads reduce injuries in side impact crashes, but federal rule may restrict their use," Dec. 27, 1997). The results consistently have demonstrated the potential of the head-protecting designs. They've produced much lower head injury measures on dummies in side-into-pole tests, for example, and in tests in which pickup trucks hit the sides of lower-riding cars.

In more recent tests in which a movable barrier struck the sides of small SUVs, the three best performers had head-protecting side airbags (see Status Report special issue: side impact crashworthiness, June 28, 2003). In contrast, none of the seven small SUVs with the worst performances had such airbags.

Effectiveness in real-world crashes

To estimate side airbag effectiveness in on-the-road crashes, Institute researchers used data from the federal Fatality Analysis Reporting System and General Estimates System to compute the relative risk of dying for drivers of 1997-2002 model cars with and without side airbags when their vehicles were struck on the left (driver) side. The researchers calculated the risk separately for side airbags with head protection versus torso-only side airbags, comparing the results with the computed risk for drivers of cars without side airbags.

Besides computing overall effectiveness estimates — 45 percent fatality reduction for drivers of cars with head-protecting side airbags, 11 percent reduction with torso-only side airbags — the researchers broke down the findings into more specific results. Lead researcher Elisa Braver notes that "side airbags with head protection reduce the risk of death for both male and female drivers over a wide span of ages. Significant protective effects were found for drivers of both large and small cars."

The effectiveness of side airbags with head protection is significant in two-vehicle collisions. Fatality risk is reduced by 53 percent. The highest estimated effectiveness (74 percent risk reduction) is in two-vehicle collisions in which passenger cars with head-protecting side airbags are struck by other cars or minivans.

"Mortality reductions also were substantial when the striking vehicles were pickup trucks or SUVs, Braver points out. "This suggests that head-protecting side airbags are addressing some of the problems of incompatibility when passenger cars are struck in the side by vehicles with higher ride heights.

O'Neill concludes that, taken as a whole, the study's findings "are compelling. It's clear that side airbags with head protection represent a very big step forward in occupant protection."

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